Cultures of adrenal medulla cells will be used to study various aspects of adrenal medulla functions. During the forthcoming year we plan to investigate the role of plasma membrane voltage-dependent mechanisms in stimulus-secretion coupling. Our results in the past year demonstrate that a membrane potential is necessary to elicit secretion of catecholamines in response to nicotine and veratridine but not in response to Ionomycin, a Ca2 ion ionophore. We will also explore in more detail the flux of Na ion and Ca2 ion into and out of the medulla cells under conditions of rest and stimulation and also further investigate the possibility that entry of Ca2 ion stimulated by nicotine and veratridine utilizes different mechanisms.